The A/C starting blowing hot after we changed out the heater valve. It was fine before!

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Some folks (whether it’s for their own car, or for a shop customer’s car), don’t experience “A/C blows hot” symptoms until after a leaking/corroded Dual Climate Control Valve (DCCV) (a.k.a. “heater valve”) is replaced. They (or their customer) worry that something they did (or even the new DCCV part) might have caused damaged to the Climate Control Module (CCM). If this has happened to you, don’t fret. It is not your fault.

There are two likely causes for a sudden shift from cold A/C to hot A/C, immediately after the DCCV is replaced:

1. Faulty new DCCV. Although rare, this can and does happen. Our customers have seen this happen first-hand, even on brand new factory OEM Bosch units. If you’re a shop that services Jaguars often, it may be best to keep a spare (newish) DCCV around, just to have as a backup or to use for comparison purposes. A new DCCV should draw approximately 0.7A when hooked up to a 12V battery when bench-tested (and also have audible, mechanical clicks when power is applied).

2. The CCM had already been damaged by the old DCCV. Sometimes, symptoms don’t manifest (appear) immediately. The CCM may have been limping along for a while. The old DCCV may have been stuck partially open (or is it partially closed?), helping to mask symptoms. It’s like not realizing that you hurt your back from yesterday’s box-moving until you woke up with back pain this morning. It’s like not feeling sick until a couple days after you sat next to someone who was exhibiting flu-like symptoms.

3. This third cause isn’t really a cause. We have heard of pristine-looking DCCV connectors (the one on the engine harness side) having poor connections. We have even heard of wires that got chewed through by rats. It’s just a reminder that the S-Type’s climate control system is no simple animal, and that anything can happen. And to better equip yourself to handle “anything,” we recommend that you: eliminate the simple or known problems first, be methodical in your problem-solving approach, use critical thinking to help think outside the box, and keep an open mind.